ARL1 belongs to the ARL (ADP-ribosylation factor-like) family of proteins, which are structurally related to ADP-ribosylation factors (ARFs). ARFs, described as activators of cholera toxin (CT) ADP-ribosyltransferase activity, regulate intracellular vesicular membrane trafficking, and stimulate a phospholipase D (PLD) isoform. Although, ARL proteins were initially thought not to activate CT or PLD, later work showed that they are weak stimulators of PLD and CT in a phospholipid dependent manner.
Histidine ammonia-lyase (HAL) is a cytosolic enzyme important in histidine catabolism. It catalyzes the nonoxidative deamination of L-histidine to trans-urocanic acid. Defective HAL activity results in accumulation of histidine and histamine in body fluids, a condition termed as hisdinemia.
